Turbocharged engines are well known in the art. A turbocharger may include a turbine wheel that is in the exhaust path of the engine. Mechanically connected to the turbine wheel is a compressor wheel that is located in the intake manifold of the engine. The engine exhaust causes the turbine wheel to rotate thereby causing the compressor wheel to compress the air entering the engine intake manifold. By compressing the air, a greater quantity of air can be introduced into the engine cylinders, thereby permitting a greater quantity of fuel to be injected, thus increasing the power output of the engine over a normally operated engine.
In some instances, compressing the air may cause too great a pressure in the intake manifold or too much pressure in the engine cylinder, which could potentially cause engine damage. Turbocharger overspeeds can also occur, possibly resulting in low cycle fatigue failures of the turbocharger after several overspeeds. A wastegate control valve may be included in order to prevent the pressure from exceeding a level at which damage might occur and to prevent overspeeds. The wastegate control valve is typically connected between the engine intake and exhaust manifolds and can be operated to allow exhaust gases to bypass the turbocharger turbine wheel so as to reduce the turbine wheel speed and thus reduce the pressure of the air which is provided to the engine cylinder via the intake manifold.
Both strictly mechanically operated wastegate control valves and electronically operable wastegate control valves are known. In the case of electronically operable wastegate control valves an electronic control module can be utilized to control the amount that the wastegate control valve is opened, and thus control the amount of exhaust gas which bypasses the turbocharger turbine wheel.
In such electronically operable wastegate control valves a problem can occur if the wastegate control valve is not operated fast enough to prevent potentially damaging conditions. For example, the electronic control module may sense the boost pressure provided by the turbocharger and deliver a wastegate control signal to the wastegate control valve in order to open the wastegate control valve if the sensed boost pressure exceeds a predetermined value. However, under some conditions the boost pressure may become high enough to cause the turbocharger to overspeed before the electronic control module responsively delivers a wastegate control signal to the wastegate control valve. A possible solution to the problem is to select a lower predetermined boost pressure at which the electronic control module acts to open the wastegate control valve. However, if such a lower boost pressure is selected engine performance may be adversely affected.
Another problem which can occur is that various component parts of the wastegate control valve can wear over time and thus the wastegate control signal required to move the wastegate control valve a given distance can also vary.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.